The invention relates to a light source and system for detecting leaks in fluid systems using light-emitting substances.
Leak detection methods have been developed to analyze fluid systems (e.g., climate control systems such as heating, cooling, ventilating, and air conditioning systems, hydraulics, engine oil systems, automatic transmission systems, fuel systems, brake systems, or radiator coolant systems) using dyes. Some methods operate by adding emissive substances (e.g., fluorescent dyes) to the refrigerants and/or lubricants of the fluid system. Suitable dyes include naphthalimide, perylene, thioxanthane, coumarin, or fluorescein, and derivatives thereof. Leaks can be detected by observing fluorescence of the dye at leak sites resulting from excitation of the dye with a light source having particular illumination characteristics (e.g., wavelength, intensity, or beam spread). Examples of leak detection methods are described in U.S. Pat. Nos. 5,357,782 and 5,421,192 which issued to Richard G. Henry on Oct. 25, 1994, and Jun. 6, 1995, respectively, both of which are assigned to the same assignee as the assignee of the present application. Similar fluorescence methods can be used in the non-destructive testing industry.
In the field of leak detection, crack detection, and related non-destructive testing, different dyes can be utilized which fluoresce at different wavelengths. Fluorescence is the emission of light at wavelengths greater than the wavelength of light emitted from the light source used to probe for leaks.
Suitable light sources for use in fluorescence detection emit light of wavelengths suitable to excite the dye and cause light emission. The visibility of the fluorescence from the dye can be increased when the leaks are illuminated with light having a wavelength between 300 and 700 nanometers. In general, the dyes fluoresce brightly when excited by light sources which emit light in the 300 to 500 nanometer range.
Typical light sources used in these types of applications include alternating current lamps operating on either 110 to 220 volts, such as the PAR 38, manufactured by Phillips. These lamps had power outputs in the 100 to 200 watt range and produced a substantial amount of light outside of the wavelength range desired to produce a good fluorescence signal. These lamps also created a large amount of heat and required the use of a ballast which provided additional bulk and weight. Self-ballasted lamps were also developed that had relatively long warm-up periods and were very sensitive to voltage surges.
In general, the invention features a light source that is small, portable, and light weight. The light source produces a narrow emission beam of light. The light source produces light having a wavelength that can effectively excite emissive substances used in leak detection systems. The light source can have a low-voltage lamp or a low heat generating lamp, such as a light emitting diode (LED).
In one aspect, the invention features a light source for examination of a substance which emits light at a wavelength greater than a wavelength of light emitted from the light source when the substance is excited by the wavelength of light emitted from the light source. The light source includes a housing having a light outlet, a reflector located within the housing, a lamp positioned in the housing between the reflector and light outlet, and a filter positioned in the housing between the lamp and the light outlet. Accordingly, the wavelength of the light emitted from the light source through the light outlet is restricted to a predetermined range effective to enhance the detection of emission of light from a substance when the substance is excited by the wavelength of light emitted from the light source. The preferred lamp is a low-voltage lamp (e.g., a halogen lamp). The preferred reflector is a parabolic reflector.
In another aspect, the invention features a light source for examination of a substance which emits light at a wavelength greater than a wavelength of light emitted from the light source when the substance is excited by the wavelength of light emitted from the light source. The light source includes a housing having a light outlet, and a low-voltage lamp positioned in the housing and oriented to emit light through the light outlet. The lamp is capable of being connected to a source of electrical power. The low-voltage lamp emits light of a wavelength within a predetermined range effective to enhance the detection of emission of light from a substance when the substance is excited by the wavelength of light emitted from the lamp. The low-voltage lamp can be a low heat generating lamp. The low-voltage lamp can be a light emitting diode.
In another aspect, the invention features a light source including a housing having a light outlet, and a low heat generating lamp positioned in the housing and oriented to emit light through the light outlet.
A filter can restrict the wavelengths of light emitted from the lamp and the light reflected by the reflector. In embodiments including a filter can employ an absorption filter, dichroic filter, or other interference filter. The filter can be part of the glass that surrounds the element of the lamp.
The lamp is capable of being connected to a source of electrical power, such as a battery, battery pack, or transformer. The reflector can be a dichroic reflector. The reflector can have a faceted surface or a smooth surface. The reflector can substantially reflect a selected wavelength of the light emitted from the lamp. For example, the reflector can reflect light primarily in the blue wavelength range, in the ultraviolet wavelength range, or in the blue and ultraviolet wavelength ranges.
In another aspect, the invention features a system for detecting leaks in fluid systems. The system includes a substance capable of emitting an emission wavelength of light after being excited by an excitation wavelength of light, and the light source, which is capable of emitting the excitation wavelength of light.
The substance can be an emissive leak detection dye, such as a naphthalimide, perylene, thioxanthane, coumarin, or fluorescein.
The system can include a filter lens for detecting the emission wavelength of light, where the emission wavelength of light emitted is enhanced by the utilization of filter lens by an observer of the emission wavelength. The filter lens can be incorporated in eyewear or a shield. The shield can be hand-held or mounted directly on the light source. When mounted on the light source, the observer can view the emission wavelength through the mounted filter lens.
The low-voltage lamp can be a high color temperature, low voltage bulb, such as, for example, a quartz halogen-xenon bulb. Small, direct current lamps of the halogen type, or similar lamps rich in gases such as xenon require no ballast, are small in dimension, are light weight, and are typically not subject to voltage surges or spiking. The low-voltage lamps provide portability. Alternatively the low-voltage lamp can be an LED or an array of LEDs.
The low-voltage lamps can be powered by batteries (e.g., 4.5V, 6V, 9V, or 12V batteries) or battery packs. The batteries or battery packs can be rechargeable. In other embodiments, the low-voltage lamp can be powered by a transformer.
Reflectors can be used to adjust the output wavelengths of light from the low-voltage lamp so that sufficient light power density (i.e., candle power density) reaches the emissive substance. The light source can include a reflector. The reflector can be a focusing reflector or a parabolic reflector. The parabolic shape of the reflector geometry can create a collimated beam consisting of parallel beams of light. The collimated beam can provide a relatively constant illumination intensity over the leak detection area.
The parabolic reflector has a three-dimensional paraboloid shape. A lengthwise cross-section of a parabolic reflector reveals a parabolic shape having a focal point. In a parabolic reflector, light rays emanating from the focal point are reflected by the surface of the paraboloid in a direction parallel to the lengthwise axis of the reflector to form the collimated beam. Because the rays are parallel, they do not noticeably diverge or converge with distance. As a result, the energy density of the light is relatively constant at short (e.g., 1 foot), medium (e.g., 3-5 feet) and long distances (e.g., up to about 100 feet) from the lamp.
The paraboloid can be described by the formula
Z=(X2+Y2)/2R
where Z is the lengthwise axis, X and Y are the perpendicular Cartesian axes, and R represents the focal point. The focal point can be between about 0.005 inches and about 2.00 inches, preferably between about 0.01 inches and about 1.50 inches. The lengthwise axis can be between about 0.3 inches and about 8 inches, preferably between about 0.5 inches and 6 inches. The corresponding diameter of the paraboloid is between about 0.50 inches and about 8 inches, preferably between about 0.75 inches and about 3 inches. The lamp is located at or near the focal point.
The reflector can have faceted or smooth surfaces to further modify light distribution. The faceted arrangement can improve the distribution of the light, or can smooth or break up light-dark edges. Facets on the surfaces of the reflector can range from fine, scarcely visible grains to clearly visible faceting, with the effect being correspondingly less or more pronounced. The reflectors can be metal (e.g., aluminum), glass, or plastic. The glass or plastic reflectors can be coated (e.g., with a metal) to obtain the particular reflective properties. The coatings can be applied, for example, by vapor deposition or plating.
Detection of fluorescence can be enhanced when the wavelength of the light emitted from the light source is restricted so that little or no light of the emission wavelength comes from the light source (e.g., little or no light beyond the excitation wavelength, extending into the visible region). The wavelength of the light emitted from the light source can be controlled by use of reflectors with faceted surfaces or dichroic coatings. The wavelength can be further influenced by passing the light through a filter before it exits the light source.
Dichroic coatings produce their reflection properties through the phenomenon of interference. The dichroic coatings consist of multiple (e.g., up to several dozen) thin layers, each only a quarter of a wavelength of the light thick, alternating between materials of a high and low refractive index. Fine tuning of the thicknesses of the layers and the way they are combined enable virtually any reflection curve to be created. The maximum reflectivity is nearly 100%, and there is virtually no absorption of radiation in the regions of low reflectivity. Accordingly, dichroic reflectors are substantially loss-free; the light that is not reflected is passed through the reflector or absorbed by the reflector.
Among the best known members of the dichroic family are the cold-light reflectors which reflect visible light between about 300 and 750 nanometers and allow radiated heat to pass unhindered through the glass. This arrangement greatly reduces thermal load on the illuminated surface or object. The reflectors can reflect the blue wavelength range and/or the ultraviolet wavelength range. In the case of the blue-light reflector, only the blue wavelength range of the spectrum (e.g., between 400 and 500 nanometers) is reflected. In the case of the ultraviolet reflector, only the ultraviolet wavelength range (e.g., between about 300 and 400 nanometers) emitted by the lamp is reflected.
Cold-light reflectors can excite emissive substances well since many emissive substances are excited by light in the wavelength range that is reflected by cold-light reflectors (i.e., 300 to 500 nanometers). Some white-light reflectors can excite emissive substances well since many emissive substances can be excited by light in the wavelength range that is reflected by the white-light reflectors (i.e, 400 to 700 nanometers). Light produced above these ranges is largely wasted since it may not produce the desired emission, produces additional heat, and can detract from the ability of an observer to see the emission wavelength. Thus, dichroic reflectors and faceted reflectors, which have narrow bandwidths of reflected light output can be used to provide proper excitation wavelengths for emissive substances and provide a precision not possible using other types of reflectors.
Lamps can also be effective at providing the wavelength range required to observe emission by providing strong intensities of light. In general, the narrower the beam spread, the greater the light power density (e.g., candle power per unit area; mW/cm2) and the greater the intensity of created emission.
It is also possible to narrow the spectral output from reflector lamps by utilizing filters. Filters can be an integral part of the reflector unit or can be independent of the reflector lamp but used in conjunction with it. An LED light source can have a narrow spectral output that does not need to employ a filter.
In general, light output from the reflector and lamp is reduced to pass only the desired wavelength for the application. Optical filters can also be used for safety purposes. Suitable filters include absorption filters, dichroic filters, or interference filters. The dichroic filters operate on the principal of interference. These filters were designed to transmit the wavelength of light which can excite the emissive substance, for example, at the site of a leak (i.e., light in the blue wavelength range or ultraviolet wavelength range).
Suitable light sources can be identified by testing the average light power density of the light in the desired spectral region for excitation at fixed distances from the light outlet (e.g., at one foot, three foot, and five foot distances). The average light power density is measured using a detector that detects light in the excitation region (e.g., a 320-400 nm detector or a 400-500 nm detector). The detector can be a radiometer such as M007-004 or a blue hazard probe such as M007-027, available from UV Process Supply, Inc. A suitable light sources has an average light power density in the ultraviolet wavelength region of at least 0.1 mW/cm2 (e.g., between 0.2 mW/cm2 and 1 mW/cm2) or in the blue wavelength region of at least 0.75 mW/cm2 (e.g., between 1 mW/cm2 and 50 mW/cm2, preferably between 5 mW/cm2 and 20 mW/cm2) at a distance of two feet or more (e.g., three feet or five feet) from the light outlet.
Additionally, it may be possible to further enhance the detection of fluorescence by observing the fluorescence through a filter lens. The filter lens can be part of a shield or eyewear used by the user of a fluorescence leak detection system. The filter lens permits only light of certain wavelengths (e.g., the emission wavelength, but not the excitation wavelength) to pass and to be detected by the user. The filter lens can take several forms, including eyewear (e.g., glasses, or goggles), or shields (e.g., face shields). The filter lens can be designed to reduce or eliminate exposure of the observer to damaging ultraviolet radiation. Thus, the filter lens, when used in combination with filters, can lead to enhanced detection of fluorescence.